This invention relates to the pyrolytic treatment of materials containing cellulose or oil in a manner to produce solid carbon and useful gases and vapors. More particularly, the invention is directed to an improved method and apparatus for carrying out the pyrolysis.
As disclosed in U.S. Pat. Nos. 4,123,332 and 4,308,103 to Rotter, the pyrolytic treatment of carbonizable materials such as saw dust, scrap tires and municipal wastes has been proposed. The pyrolysis process consists of heating the feed materials in order to drive off and recover gases such as methane and hydrocarbon vapors while leaving solid carbon materials which are also recovered. The primary problem with the machines and processes that have been proposed in the past is their inefficiency. In order to heat the feed materials sufficiently to produce end products having acceptable purity, it is necessary to burn an excessive amount of fuel. Consequently, the overall process has not been practical from an economic standpoint. Handling of the combustion gases has also been a problem.
The present invention provides an improved pyrolysis process and improved equipment which eliminates much of the inefficiency associated with the processes and machines that have been proposed in the past. In accordance with the invention, a multiple stage pyrolysis unit is equipped with a plurality of reaction cylinders which are arranged at different levels and which receive the carbonizable materials in succession. Solid fuel is burned in a firebox of the unit to heat the reaction cylinders and their contents. The arrangement of the successive reaction cylinders at different levels enhances the thoroughness and uniformity with which the feed materials are heated to create efficiencies that have not heretofore been achieved.
Additionally, the process gas which is produced in each reaction cylinder is passed through the carbonizable materials in the preceding cylinders, thereby further heating the materials and improving the efficiency of the heat utilization. The feed materials are agitated as they are conveyed through the reaction cylinders so that the process gas can intimately contact and transfer heat to the materials. The process gas is heated in manifolds which underlie the cylinders and is injected into each cylinder through a series of slots which distribute the gas uniformly in the cylinder. Baffles which overlie the slots deflect the solid carbonizable materials away from the slots to prevent the solids from passing through the slots into the gas manifolds.
A further important feature of the invention is the provision of a unique feeder unit which feeds both the fuel and the carbonizable material to the pyrolysis unit. In the feeder, the hot combustion gases that result from burning of the fuel are passed through both the incoming fuel and the incoming feed materials. This both dries and preheats the incoming materials an also filters the exhaust gases prior to their discharge. In the drying zones of the heater, unique inclined surfaces are provided with baffled openings to permit the combustion gases to thoroughly and intimately contact the fuel and feed material. The fuel is also passed through a drying cylinder in which the combustion gases are applied to the fuel as it is being conveyed through the drying cylinder and simultaneously agitated.
The physical configuration of the pyrolysis unit and the improved manner in which heat is transferred to the feed materials creates efficiencies that make the pyrolysis process economically feasible. At the same time, the process produces substantially pure carbon and permits the recovery and use of virtually all recoverable gases and vapors while discharging relatively clean exhaust gases.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.